1. Field of the Invention
The present invention relates to a synthetic derivative of the proinsulin C peptide. Proinsulin comprising this derivative has properties which are better in various ways than conventional monkey proinsulin, in particular the final yield of the particular insulin derivative is improved on recombinant preparation thereof.
2. Description of the Related Art
The number of patients with diabetes is continually increasing around the world. There is a proportionate increase in the demand for insulin or derivatives of insulin. Thus the object is to optimize the existing processes in relation to the yield of active ingredient. European patent EP-B1 0 489 780 proposes a process for preparing insulin or derivatives thereof. The vectors described therein are used to prepare human insulin with the plasmid pINT90d or else starting plasmids for constructing the plasmid pINT302d which is described in European patent application EP-A 0 821 006 and is used for preparing a His(B31) His(B32) Gly(A21)-insulin derivative, or to construct the vector pINT329d, which is described in European patent application EP-A 0 885 961 and is used for preparing the Lys(B3) Glu(B29)-insulin derivative.
The instant invention therefore provides a precursor of human insulin or a precursor of an insulin analog of the formula I:
Fus-B(1-0)-RDVP-Yn-A(1-21)xe2x80x83xe2x80x83(I);
wherein
Fus is an optionally present fusion portion;
B(1-30) is a B chain of human insulin,
Y is an amino acid chain which terminates with a basic amino acid at the C terminus;
n is from 2 to 50 and indicates the length of the amino acid chain Y; and
A(1-21) is an A chain of human insulin,
and the A chain and/or the B chain can be modified by amino acid substitutions, deletions and/or additions.
In one embodiment, Yn is amino acids 5 to 35 of a C peptide of human or monkey insulin.
In another embodiment, Yn is amino acids 11 to 35 of human insulin.
In another embodiment, the B chain of human insulin comprises: Lys(B3)Glu(B29).
In another embodiment, the B and A chains of human insulin comprise: His(B31)His(B32)Gly(A21).
The instant invention also provides DNA encoding for those precursors of the instant invention.
The instant invention also provides a vector comprising a DNA encoding for those precursors of the instant invention.
In one embodiment, the vector is an expression vector suitable for expression in a host cell, preferably E. coli. 
The instant invention also provides for a host cell comprising a vector comprising a DNA encoding for those precursors of the instant invention. Preferably the host is E. coli. 
The instant invention also provides for a process for preparing a precursor of the instant invention, comprising the steps of:
a) introducing a DNA coding for the instant precursors into a vector;
b) introducing the vector from (a) into a host cell;
c) allowing the host cell to express the precursor into a culture supernatant; and
d) isolating the precursor from the culture supernatant.
The instant invention also provides for a process for preparing DNA, comprising the steps of:
a) producing a DNA from a cDNA of human or monkey insulin by PCR; and
b) isolating said DNA;
wherein said DNA encodes a precursor of the instant invention.
The instant invention also provides for a process for preparing human insulin or an insulin analog, comprising the steps of:
a) preparing a said precursors by the instant processes of the instant invention;
b) forming disulfide bridges in the precursor by allowing the precursor from (a) to fold;
c) optionally enzymatically cleaving the fusion portion Fus; and
c) purifying the human insulin or the insulin analog.
It has now been found that particularly advantageous proinsulin derivatives are those of the formula I,
Fus-B(1-30)-RDVP-Yn-A(1-21)xe2x80x83xe2x80x83(I);
wherein
Fus is an optionally present fusion portion of any suitable sequence;
B(1-30) is the B chain of human insulin,
Y is an amino acid chain which terminates with a basic amino acid at the C terminus;
n is from 2 to 50 and indicates the length of the amino acid chain Y; and
A(1-21) is the A chain of human insulin,
and wherein the A chain and/or the B chain can be modified by amino acid substitutions, deletions and/or additions. It is surprising in this connection that equal and mutually different advantages are observed depending on the composition of the insulin A or B chain.
Connection of the human B chain to the human A chain via the advantageous C peptide results in a proinsulin which behaves in terms of expression yield like wild-type proinsulin, but its enzymatic processing to insulin can be controlled more easily so that no disruptive traces of B chain extended by arginine are produced and have to be removed during preparation to give the pharmaceutical, causing losses of yield.
On connection of the B chain with a C-terminal di-histidine extension to the A chain of human insulin containing glycine in position A21 using the C peptide according to the invention there is found to be an expression yield which is about 20% higher than the yields which can be achieved with the plasmid pINT90d and a yield which is almost five times higher than observed with the plasmid pINT302d. In addition, control of the enzymatic processing is simplified in the same way as previously described.
On connection of a Lys(B3) Glu (B29)-modified B chain to the A chain of human insulin via the modified C peptide there is found to be improved folding properties of the proinsulin derivative compared with the proinsulin encoded by pINT329d. The yield of crude fusion protein is increased and reaches the same level as found with the plasmid pINT90d. In addition, control of the enzymatic processing is simplified.
A particularly advantageous embodiment of the novel C peptide is characterized by the following amino acid sequence: CGCGATGTTCCTCAGGTGGAGCTGGGCGGGGGCCCTGGCGCAGGCAGCCTGCAGCCCTTG RDVPQVELGGGPGAGSLQPL GCGCTGGAGGGGTCCCTGCAGAAGCGC (SEQ ID NO.: 1)
ALEGSLQKR (SEQ ID NO.: 2)
One of many possible DNA sequences coding for the indicated C peptide is likewise indicated.
One aspect of the invention is a precursor of human insulin or of an insulin analog of the formula I
Fus-B(1-30)-RDVP-Yn-A(1-21)xe2x80x83xe2x80x83(I);
wherein
Fus is an optionally present fusion portion of any suitable sequence;
B(1-30) is the B chain of human insulin,
Y is an amino acid chain which terminates with a basic amino acid at the C terminus;
n is from 2 to 50 and indicates the length of the amino acid chain Y; and
A(1-21) is the A chain of human insulin,
and wherein the A chain and/or the B chain can be modified by amino acid substitutions, deletions and/or additions, in particular where Yn is amino acids 5 to 35 of the C peptide of human or monkey insulin, preferably where Yn is amino acids 11 to 35 of human insulin.
Another aspect of the invention are precursors as described above, where the B chain of human insulin comprises the modifications Lys(B3) Glu(B29) or where the B and A chains of human insulin comprise the modifications His(B31) His(B32) Gly(A21).
The instant invention includes substitutions, additions, or deletions, of one or more amino acid residues of the claimed precursor of human insulin or precursor of an insulin analog of formula I.
Substitutional variants typically contain the exchange of one amino acid for another at one or more sites within the protein, and are designed to modulate one or more properties of the protein such as stability against proteolytic cleavage. Substitutions preferably are conservative, that is, one amino acid is replaced with one of similar shape and/or charge. Conservative substitutions are well known in the art and include, but are not limited to, the changes of: alanine to serine; arginine to lysine; asparigine to glutamine or histidine; aspartate to glutamate; cysteine to serine; glutamine to asparigine; glutamate to aspartate; glycine to proline; histidine to asparigine or glutamine; isoleucine to leucine or valine; leucine to valine or isoleucine; lysine to arginine, glutamine, or glutamate; methionine to leucine or isoleucine; phenylalanine to tyrosine, leucine or methionine; serine to threonine; threonine to serine; tryptophan to tyrosine; tyrosine to tryptophan or phenylalanine; and valine to isoleucine or leucine.
Addition variants contain fusion proteins such as those used to allow rapid purification of the protein and also can include hybrid proteins containing sequences from other proteins and polypeptides which are homologues of the protein.
Deletion variants, for example, lack one or more residues of the protein which are not essential for immunogenic activity or biological activity.
The present invention may also include such non-conservative additions, deletions or substitutions that do not destroy biological activity. Those persons skilled in the art, using established procedures to detect desired biological activity similar to insulin, can readily determine which amino acid residues may be added, deleted, or substituted, for example, by the measurement of biochemical activity of the polypeptides using conventional biochemical assays, such as in vitro assays detecting signal transduction in a biochemical pathway in which insulin is implicated. Alternatively, non-conservative substitutions may be made at positions in which, for example, alanine-scanning mutagenesis reveals some tolerance for mutation in that substitution of an amino acid residue with alanine does not destroy biological activity. The technique of alanine scanning mutagenesis is described by Cunningham and Wells, Science, 1989, 244:1081, and incorporated herein by reference in its entirety.
Well established preparatory techniques of the above-described variants are within the skill of the artisan. These procedures include, for example, conventional methods for the design and manufacture of DNA sequences coding for bacterial expression of the instant polypeptides, the modification of cDNA and genomic sequences by site-directed mutagenesis techniques, the construction of recombinant proteins and expression vectors, and bacterial expression of the polypeptides. These procedures are described, for example, in CURRENT PROTOCOLS IN MOLECULAR BIOLOGY, Ausubel et aL Eds. (John Wiley and Sons, New York, 1987).
The optional fusion portion includes those conventional fusion proteins that increase levels of expression, increases protein longevity, provides an efficient way of purification, or alternatively, are known selectable markers that are easily assayed for monitoring efficiency of both eucaryotic and procaryotic expression. Preferably, the instant fusion portion is protected against proteolytic degradation, allows a high yield of fusion protein, is easily soluble, does not impair folding of the fusion protein during conversion to mature insulin, allows enzymatic removal from the A- and B-chains in a one-pot reaction in which the C-chain is removed from the precursor, allows purification of the precursor by, for example, affinity chromatography, and is easily separated from insulin.
The artisan will readily recognize that those methods for preparing fusion proteins are well known in the art. Examples of such fusion protein expression systems are the glutathione S-transferase system (Pharmacia, Piscataway, N.J.), the maltose binding protein system (NEB, Beverley, Mass.), the FLAG system (1B1, New Haven, Conn.), and the 6xc3x97His system (Qiagen, Chatsworth, Calif.). Some of these systems produce recombinant protein bearing only a small number of additional amino acids, which are unlikely to affect the antigenic ability of the recombinant protein. For example, both the FLAG system and the 6xc3x97His system add only short sequences, both of which are known to be poorly antigenic and which do not adversely affect folding of the protein to its native conformation. Other fusion systems produce proteins where it is desirable to excise the fusion partner from the desired protein. The fusion partner may be linked to the recombinant protein by a peptide sequence containing a specific recognition sequence for a protease. Examples of suitable sequences are those recognized by the Tobacco Etch Virus protease (Life Technologies, Gaithersburg, Md.) or Factor Xa (New England Biolabs, Beverley, Mass.). Fusion protein expression systems are also described in U.S. Pat. Nos. 5,227,293 and 5,358,857.
A further aspect of the invention is a DNA coding for a precursor as described above.
Likewise an aspect of the invention is a vector comprising a DNA coding for a precursor as described above, preferably wherein the vector is an expression vector suitable for expression in host cell such as E. coli. Such vectors include PET vector systems (Stratagene), pSE vector systems (Invitrogen), and PROLar vector systems (Clonentech).
A further aspect of the invention is a host cell such as E. coli comprising a vector as described above. Suitable host cells are well known to the skilled artisan.
A further aspect of the invention is a process for the preparation of a precursor as described above, where
(a) a DNA as described above is introduced into a vector as described above;
(b) the vector from (a) is introduced into a host cell;
(c) the host cell from (b) comprising the vector from (a) is used for expression: and
(d) the precursor is isolated from the culture supernatant.
Preferably, the host is E. coli. 
An additional aspect of the invention is a process for preparing a DNA as described above, where
(a) this DNA is produced starting from the cDNA of human or monkey insulin by means of PCR and other molecular biology techniques, and
(b) is isolated.
A further aspect of the invention is a process for preparing human insulin or an insulin analog, where
(a) a precursor as described above is produced by the process as described above;
(b) the precursor from (a) is folded under suitable conditions so that the disulfide bridges can form as in human insulin, and the RDVP-Yn part and, where appropriate, the fusion portion Fus is deleted enzymatically; and
(c) the human insulin or the insulin analog is purified.
A further aspect of the invention is the use of a precursor as described above for preparing insulin or an insulin analog, preferably where the preparation of insulin or an insulin analog takes place by the process as described above.
It is a further aspect of the invention to use a DNA as described above for preparing a precursor as described above.
One aspect of the invention is also the use of a vector as described above for preparing a precursor as described above.
A further aspect of the invention is the use of an E. coli cell as described above for preparing a precursor as described above. Suitable E. coli strains are, for example, BL 21, HB101, TOP10F (all from Invitrogen), DH5alpha (Clonentech), TOPP, JM109 (both from Stratagene).
The invention is now explained in detail by means of examples without, however, being restricted thereto.